Remember that full frame is not explicitly better than APS-C, it's just 'different'.
It's perceived as better because shallow depth of field is very trendy, and that's the advantage of full frame, and for the portrait work I do it's invaluable, and even more important is the fact that I can shoot a scene at f2.8 and have it sharp, if I shoot the same scene on a crop and want the same bokeh then I have to shoot at f1.4 and it's significantly softer.
In fact, if you need maximum depth of field then full frame becomes a disadvantage. For example I shoot 3 or 4 models at a time and need the depth of field to cover them, this requires a very small aperture- like f8, this then requires a lot of light to fill the scene. If I shot the same scene with a crop camera I can get away with f5.6, and half the lighting power- the tradeoff being that the 5d files will be sharper, and allow me to crop in more, but if the shoot doesn't have the budget to cover the lighting costs then the small increase in sharpness is moot.
I shoot both full frame and APS-C because I need to use them both for different purposes. I'm even considering dropping down to micro 4/3 because I could have a use for that too (i.e. maximum depth of field at large apertures with minimal lighting)